Originally Posted By: CATERHAM
Originally Posted By: Gokhan
Originally Posted By: MMasz
It won't harm your engine. In Europe they recommend anything between 0W-20 and 20W-50 for engines that strictly call for 0W-20 in US.
You will see most benefits from 5W-40 if you drive hard or do towing. Most engine damage occurs because of oil-film breakdown during high acceleration from a full stop. 5W-40 will help if this is your driving habit. Otherwise, 5W-20 should be OK for gentle driving and no towing, no uphill driving, etc.
As far as fuel economy is concerned, you will see little difference if you drive hard. If you drive gently, you will see about 1 MPG drop from switching to 5W-40.
If you do switch, Rotella T6 should be a good choice.
Poor misleading advice.
No matter how hard ( meaning fast) you drive or how heavy a trailer you may tow is, there is ZERO benefit and many disadvantages (in addition to the 4 to 10% fuel economy drop) to running an oil two grades heavier than what the manufacturer (Ford) recommends. The reason is that it you will not be able to acheive oil temp's high enough to thin out the 40wt oil into the optimum range.
Even with the spec' 5W-20 oil, 99% of the time the oil will be thicker than optimum that's how high the viscosity safety margin is with the allegedly light oil grade.
But don't take my word for it, there isn't a well regarded member on this board that would support the notion.
You're only thinking about oil pressure and flow at high RPM. Most engine wear occurs not at high RPM but at low RPM and high torque -- in other words, acceleration from a full stop. In order to prevent metal - metal contact at such conditions, which is known as boundary lubrication, where the only protection is antiwear additives that coat the metal parts, you need to have a sufficient high-temperature, high-shear (HTHS) viscosity to prevent oil-film breakdown due to low RPM, low viscosity, and high torque. (Oil-film thickness is directly proportional to viscosity and rate of shear [RPM] and inversely proportional to torque.)
As I said before, in Europe, all grades between 0W-20 and 20W-50 are recommended for most engines that strictly call for 0W-20 in North America -- a whole range of four steps in oil viscosity.